<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        let str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

        let cites = [
            { py: 'beijing', name: '北京' },
            { py: 'alishan', name: '阿里山' },
            { py: 'beidaihe', name: '北戴河' },
            { py: 'shijiazhuang', name: '石家庄' }
        ]

        
        let obj = {};
        str.split('').forEach(function (item, index) {
            obj[item] = []
        })
        console.log(obj);
       
        cites.forEach(function(item,index){
            // console.log(obj[cites[index].py.slice(0,1).toLocaleUpperCase()]);
            obj[cites[index].py.slice(0,1).toLocaleUpperCase()].push(cites[index])
        })
    /*
        let datas = {
                A:[],
                B:[],
                C:[],
                ...
            }     
    */
    </script>
</body>

</html>